Implement client-server integration tests for KMIP operations

[smira]

In server_test.go, there's a set of simple tests which exercise basic error handling using DISCOVER_VERSIONS operation, but that could be extended to test major flows, like CREATE_KEY, GET_KEY, etc.

Another idea might be to do integration test with pykmip being the client and go-kmip implementing fake KMIP server (or vice versa).